This invention relates to a heat exchanger that utilizes a high temperature aluminum subject to thermal fatigue due to heat cycles.
Aircraft air management systems utilize heat exchangers to provide cooling and/or heating for various components as well as cabin comfort. In an effort to reduce the weight of the systems, aluminum is used as the material of choice for some of the high operating temperature heat exchangers. Recent applications have exposed the aluminum heat exchangers to even higher temperatures. The result is a greater possibility for failures due to thermal fatigue.
To minimize structural failures and increase reliability, it has been shown that restricting cold side flow to certain areas of the cooling core within the heat exchanger reduces thermal stresses and thus thermal fatigue. A piece of sheet metal is typically used to serve as a blocking surface to divert flow around a portion of the heat exchanger that is typically subject to thermal fatigue. Welding the sheet metal to the core about its perimeter is not feasible because the welds cracked due to thermal stresses during the heat cycles.
To address this problem, the sheet metal has been secured to the core using a high temperature RTV to permit thermal expansion of the core. The sheet metal is also riveted to the heat exchanger since the RTV alone cannot reliably secure the sheet metal to the core over time.
The core must be cleaned so that the RTV can securely bond the sheet metal to the core. The additional time, preparation, and materials needed to secure the sheet metal to the core with this method adds cost to the heat exchanger. What is needed is an improved method and apparatus for providing the blocking surface on the heat exchanger.